Capacitor-less power supply

ABSTRACT

The present disclosure provides a capacitor-less AC/DC converter power supply system. The power supply system includes one or more rectifier cells having inductive and synchronous elements, and removing any capacitive filter elements thus ensuring a very high Mean Time Before Failure (MTBF) on the rectifier stage. The output voltage and current generated by the one or more inductive cells is a DC signal having a ripple amount dependent upon the number of cells implemented.

TECHNICAL FIELD

The present disclosure relates to power supply systems, and moreparticularly, to power supply systems that eliminate capacitors.

BACKGROUND

Peak rectifier circuits change AC into pulsed DC by eliminating thenegative half-cycles or alternating the AC voltage. Only a series ofpulsations of positive polarity remain. Conventional rectifiers areclassified according to the number of AC conducted positive half-cycles(i.e. half-wave rectifiers or full-wave rectifiers). Two types ofcircuits are used for full-wave, single-phase rectification: One circuituses a transformer with a mid-tap in the secondary winding and a pair ofrectifier diodes; the other uses a bridge diode configuration whichrequires two extra rectifier diodes and, in case of employ a transformerafter the AC input voltage, the secondary requires only half as muchwinding. Performances are similar except that the bridge diodes aresubjected to only half the peak inverse voltage of the center-tapcircuit.

As both halves of the cycle are rectified, the current and voltage onthe input side are normal effective values; RMS values on the outputside are the same as for a sine wave while the DC or average values aretwice that of a half-wave circuit. A Fourier analysis of the rectifieroutput waveform yields a constant term (DC voltage) and a series ofharmonic terms. Filters are usually added to extract the constant termand attenuate harmonic terms. Inductor-input filters are preferred inhigher-power applications in order to avoid excessive turn-on andrepetitive surge currents. However, the use of an inductor alone isgenerally impractical, particularly when variable loads must be handledbecause the attenuation is not sufficient with reasonable values ofinductance. When capacitor-input filters are used, diodes whose averagerating more nearly matches the load requirement can be used if asource-to-load resistance ratio of about 0.03 and voltage regulation ofabout 10% are acceptable. A capacitor-input filter has a shunt capacitorpresented to the rectifier output. Each time the positive peakalternating voltage is applied to one of the rectifier anodes, the inputcapacitor charges up to just slightly less than this peak voltage.

No current is delivered to the filter until another anode approaches itspeak positive potential. When the capacitor is not being charged, itsvoltage drops off nearly linearly with time because the load draws asubstantially constant current. Use of an input capacitor increases theaverage voltage across the output terminals of the rectifier and reducesthe amplitude of the ripple in the rectifier output voltage. In anycase, the capacitor charges up to the peak voltage of the rectifieroutput during the time that current pulses are delivered to the filterload. If the capacitance is large, more energy is stored during currentpulses and the capacitor output voltage remains relatively high duringdischarge. On the other hand, if the load current is large, thecapacitor discharges rapidly between current pulses and the average DCoutput voltage falls to a low value. This continuous charge-dischargecycle stress imposed on the filter capacitor contributes to the aging ofthe device and eventually to its failure. Replacing capacitorsperiodically is the only way to insure a very high Mean Time BeforeFailure (MTBF) for capacitors.

DC Aluminum electrolytic capacitors use an aluminum oxide layer as thedielectric and a dielectric grade aluminum foil as the current inputbias. Both the materials and the processing have non-uniformities on asmall scale. Two elementary mechanisms lead to capacitor field aging.The first is due to the leakage currents and the second one has to dowith physical conditions such combinations of heat and chemicalcontaminant.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of various embodiments of the claimed subjectmatter will become apparent as the following Detailed Descriptionproceeds, and upon reference to the Drawings, wherein like numeralsdesignate like parts, and in which:

FIG. 1 illustrates an example power supply system consistent withvarious embodiments of the present disclosure;

FIG. 2 illustrates a timing diagram for various signals in connectionwith the operation of the power supply system of FIG. 1;

FIG. 3 illustrates a power supply system according to other embodimentsof the present disclosure; and

FIG. 4 illustrates a timing diagram of a simulation of a 2-cell powersupply system of FIG. 1 or FIG. 3.

Although the following Detailed Description will proceed with referencebeing made to illustrative embodiments, many alternatives, modificationsand variations thereof will be apparent to those skilled in the art.

DETAILED DESCRIPTION

FIG. 1 illustrates an example power supply system 100 consistent withvarious embodiments of the present disclosure. The power supply system100 of FIG. 1 represents a AC/DC converter system, for example, togenerate DC output voltage (V_(O)) and current (I_(O)) from an inputvoltage source 116 (Vin), the input voltage 116 may include a sinusoidalsuch as conventional wall outlet voltage sources (e.g., 110 VAC, etc.),and/or square signal source as in a switched-mode power supply (SMPS)equipment. The power supply system 100 includes a plurality of inductivecells 102A and 102B. Although two inductive cells 102A and 102B areshown in FIG. 1, it is to be understood that the power supply system100, in other embodiments, may be extended to n number of cells; where nis an even number. Multiple cells may reduce a ripple of the DC outputvoltage, but may increase cost and/or complexity of the system 100. Ingeneral, the number of cells for a given implementation may depend on,for example, the load tolerance to ripple, etc. Each inductive cell 102Aand 102B includes inductive coupled elements 110A, 112A and 110B, 112B,respectively, and a synchronous rectifier circuitry 114A and 114B,respectively. The inductive coupled elements 110A, 112A and 110B, 112Bmay each include, for example, transformer circuitry, etc., and thepolarity of the inductive elements are coupled in a “same” polarityconfiguration, as shown. The synchronous rectifier circuitry 114A and114B may each include, for example, diode circuitry as shown. In otherembodiments, the synchronous rectifier circuitry 114A and 114B mayinclude, for example, switch elements (e.g., MOSFET devices) having bodydiode elements biased in a similar manner. In such an embodiment,controller circuitry (not shown) may be provided to control theconduction state of the switch elements based on, for example, thevarious operating modes described below. In at least one embodiment, theinductive coupled elements 110A, 112A and 110B, 112B may each havesimilar electrical characteristics, e.g., impedance, inductance, etc.,and may each be similarly sized. Of course, similar in this sense maydepend on tolerance requirements for a given implementation. The diodecircuitry 114A, 114B may also have similar electrical characteristics.

The power supply system 100 also includes input transformer circuitry104 having a primary side 106 coupled to Vin, and a plurality ofsecondary sides, e.g., 108A and 108B. Secondary side 108A is coupled toinductive element 110A of cell 102A and inductive element 110B of cell102B. Secondary side 108B is coupled to inductive element 112A of cell102A and inductive element 112B of cell 102B. The number of secondarysides 108A and 108B may generally correspond to the number of inductivecells 102A and 102B. The secondary sides 108A, 108B are coupled to theprimary side 106 in a “same” polarity configuration, as shown. The inputtransformer circuitry 104 is generally provided to reduce Vin (stepdown) and to provide Vin to each of the inductive cells 102A, 102B in analternating fashion. The turns ratio of 108A and 108B may be the same orsimilar, so that the voltage of the secondary side of transformer 104 isalternating between 108A and 108B. As shown in FIG. 1, the dot side of108A is coupled to the cathode of 114A and the dot side of 108B iscoupled to the anode of 114B, thus creating an alternating conductionbetween cells 102A and 102B. In at least one embodiment, thestepped-down voltage provided by each secondary side 108A, 108B may besimilar, e.g., the number of windings of each of the secondary sides108A, 108B is the same or approximately the same. Diode circuitry 114Ais coupled between a positive terminal of secondary side 108A and anegative terminal of secondary side 108B, forward biased towardinductive element 110A. Diode circuitry 114B is coupled between anegative terminal of secondary side 108A and a positive terminal ofsecondary side 108B, forward biased toward inductive element 110B.

For an even number of inductive cells, 2, 4, 6 . . . n, an outputcurrent ripple frequency will generally be the double of the frequencyin Vin. This may be beneficial due since the ripple is smaller, andtherefore the inductive cells act as ripple filters, without the needfor filtering capacitor stages. In addition, the inductive cells providefull-wave rectification of the input voltage.

FIG. 2 illustrates a timing diagram 200 for various signals inconnection with the operation of the power supply system of FIG. 1. Thetime period [−t₁, t₃] represents a commutation period, T_(S), of thesecondary sides 108A, 108B of the input transformer 104. (T_(S) may alsobe defined in time period [t₀, t₄], but for purposes of this embodimentT_(S) is defined in time period [−t₁, t₃]). Waveform 202 represents thecell voltage of inductive cell 102A (negative portions) and inductivecell 102B (positive portions), V_(Cell1, 2). Waveform 204 represents thecurrent of the inductive coupled elements 110A, 112A of cell 102A,i_(110A, 112A). Waveform 206 represents the voltage across the diode114A of cell 102A, V_(D1). Waveform 208 represents the current of theinductive coupled elements 110B, 112B of cell 102B, i_(110B, 112B).Waveform 210 represents the voltage across the diode 114B of cell 102B,V_(D2). The solid signals of waveform 212 represent the current throughthe diode 114A of cell 102A, I_(D1), and the broken-line signals ofwaveform 212 represent the current through the diode 114B of cell 102B,I_(D2). Waveform 214 represents the output current, I_(O), and waveform216 represents the output voltage, V_(O). With continued reference tothe power supply system of FIG. 1 and the timing diagram of FIG. 2,various operational states are described below:

State I[−t₁, t₀] and [t₁, t₂]:

This state occurs when the voltage of secondary sides 108A and 108B areapproximately equal to 0, which corresponds to when the AC input isapproximately zero. In this state, the power supply 100 can generally beconsidered to be in a freewheeling state. In State I, diodes 114A and114B are in forward bias, since the voltage stored in inductive elements112A and 112B exceeds the positive voltage of the secondary sides 108Aand 108B. The current generated by inductive cell 102A is continuing toramp down, as shown by waveform 204. Similarly, the current generated byinductive cell 102B begins to ramp down, as shown by waveform 208. Thevoltage across diodes 114A and 114B is approximately zero, as shown bywaveforms 206 and 210, respectively. The current through diode 114Abegins ramping down during the period [−t₁, t₀], as energy stored ininductive element 112A dissipates, and begins ramping up during theperiod [t₁, t₂] as energy stored in inductive element 112A begins toincrease, as shown by waveform 212 (solid lines). The current throughdiode 114B begins ramping up during the period [−t₁, t₀], as energystored in inductive element 112B increases, and begins ramping downduring the period [t₁, t₂] as energy stored in inductive element 112Bbegins dissipates, as shown by waveform 212 (dashed lines). Outputcurrent (I_(O)) and output voltage (V_(O)) begin to decrease duringthese periods, but remain positive and therefore supplying power to aload, as shown by waveforms 214 and 216, respectively. The maximum peakcurrent delivered by each cell, as indicated by i_(110Amax) of waveform204, is based on the input voltage (Vin), load impedance (R_(O)) andtime, as described in detail below. The minimum current delivered byeach cell, as indicated by i_(110Amin) of waveform 204, is based on theinput voltage (Vin), load impedance (R_(O)) and time, as described indetail below. The total output current, I_(O), is generated by the sumof current from each cell. Waveforms 204, 208 and 214 are depicted asnormalized, and may have different values depending on particularoperating conditions. Waveform 214 is a composite (sum) of waveforms 204and 208.

State II[t₀, t₁]:

State II begins when the voltage of cell 102A is positive (waveform202), and diode 114A is in a reverse bias state and diode 114B is in aforward bias state. The voltage across diode 114A is positive (waveform206), and the current through cell 102A ramps up from i_(110Bmin) toi_(110Bmax) during this period (waveform 204). The voltage across diodeD₂ (114B) is approximately zero (waveform 210), and the current throughcell 102B continues to decrease (waveform 208). The current throughdiode 114A is approximately zero (waveform 212—solid lines) and thecurrent through diode 114B is at the maximum (waveform 212—dashedlines). Output current, I_(O), is provided by cell 102B. Thus, currentof cell 102B (waveform 208) is discharging and decreasing while theoutput load current (waveform 214) is increasing.

State III [t₂, t₃]:

State III is similar to State II, and begins when the voltage of cell102B is negative (waveform 202), and diode 114B is in a reverse biasstate and diode 114A is in a forward bias state. The voltage acrossdiode 114A is approximately zero (waveform 206), and the current throughcell 102A continues to decrease from State I (waveform 208). The voltageacross diode D₂ (114B) is positive (waveform 210), and the currentthrough cell 102B ramps up from i_(110Amin) to i_(110Amax) during thisperiod (waveform 208). The current through diode 114A is at a maximum(waveform 212—solid lines) and the current through diode 114B isapproximately zero (waveform 212—dashed lines). Output current, I_(O),is provided by cell 102A Thus, current of cell 102A (waveform 204) isdischarging and decreasing while the output load current (waveform 214)is increasing.

Advantageously, the output current (I_(O)) and the output voltage(V_(O)) are rectified DC signals with low ripple and are generatedwithout the use of any capacitive elements. Thus, the power supplysystem described herein may offer increased mean time between failures(MTBF) performance due to non-aging elements of the power supply.

FIG. 3 illustrates a power supply system 300 according to otherembodiments of the present disclosure. As described above with referenceto FIG. 1, the power supply system 100 may include n number of inductivecells. As the number of cells increase, the ripple of the output voltage(V_(O)) and output current (I_(O)) may decrease. Accordingly, FIG. 3illustrates a supply system having n number of cells, Cell₁, Cell₂ . . .Cell_(n), where n is an even number. The coupling of the variouselements of each cell is illustrated. Also, in this embodiment, thenumber of secondary sides of the input transformer circuitry generallycorrespond to the number of cells.

FIG. 4 illustrates a timing diagram 400 of a simulation of a 2-cellpower supply system of FIG. 1. Similar to the timing diagram of FIG. 2,Waveform 402 represents the cell voltage of inductive cell 102A(negative portions) and inductive cell 102B (positive portions),V_(Cell1, 2). Waveform 404 represents the current of the inductivecoupled elements 110A of cell 102A, i_(110A). Waveform 406 representsthe voltage across the diode 114A of cell 102A, V_(D1). Waveform 408represents the current of the inductive coupled elements 110B of cell102B, i_(110B). Waveform 410 represents the voltage across the diode114B of cell 102B, V_(D2). The solid signals of waveform 412 representthe current through the diode 114A of cell 102A, I_(D1), and thebroken-line signals of waveform 412 represent the current through thediode 114B of cell 102B, I_(D2). Waveform 414 represents the outputcurrent, I_(O), and waveform 416 represents the output voltage, V_(O).

Design Considerations

With continued reference to FIGS. 1 and 2, taking into account thatCell₁ corresponds to 102A and Cell₂ to 102B; the following conditionsfor the steady-state analysis of the power supply system 100 areassumed: the power source from the primary side is an ideal AC voltagesource, inductors are designed to operate in continuous inductor currentmode (CICM), all semiconductors are ideal and passive components do notcontain stray elements, the output voltage is constant during acommutation period T_(S), and the operative modes are referenced to theinput voltage according to time interval Δt_(i) from the period [t_(i),t_(i+1)].

The behavioral result of the proposed circuit with the currentsi_(110Amin) and i_(110Amax) as the difference of current in theinductive cell 102A for an output resistive impedance R_(O) are givenas:

${i_{110A_{\min}} = {{\frac{V_{102A}}{R_{O}}\left\lbrack \frac{e^{{kt}_{on}} - 1}{e^{k} - 1} \right\rbrack} - I_{O}}};{i_{110A_{\max}} = {{\frac{V_{102A}}{R_{O}}\left\lbrack \frac{e^{{kt}_{off}} - 1}{e^{- k} - 1} \right\rbrack} - I_{O}}}$$\mspace{20mu}{{\Delta\; I_{102A}} = {{{{i_{110A_{\max}} - i_{110A_{\min}}}}\mspace{20mu}\therefore\;{\Delta\; I_{102A}}} = {\frac{V_{102A}}{R_{O}}\left\lbrack \frac{1 - e^{- {kt}_{on}} + e^{- k} + e^{- {kt}_{off}}}{1 - e^{- k}} \right\rbrack}}}$for k=(T _(S) R _(O))/L

Where t_(on) is defined as the interval [t₀, t₁] and t_(off) is [t₁, t₄]as shown in FIG. 2. Considering all the powering operative modes andextending for n cell number, the following may be affirmed:I _(102A) =I _(110A) −I _(112A) ;I _(102B) =I _(110B) −I _(112B); . . .where, I_(Cell 1)=I_(102A); I_(Cell 2)=I_(102B); . . .

${\overset{yields}{\Longrightarrow}I_{O}} = {\sum\limits_{n = 1}I_{{cell}_{n}}}$With an I_(O) ripple frequency twice the current ripple frequency 204.

“Circuitry”, as used in any embodiment herein, may comprise, forexample, singly or in any combination, hardwired circuitry, programmablecircuitry such as computer processors comprising one or more individualinstruction processing cores, state machine circuitry, and/or firmwarethat stores instructions executed by programmable circuitry. Thecircuitry may, collectively or individually, be embodied as modules thatform part of a larger system, for example, an integrated circuit (IC),system on-chip (SoC), desktop computers, laptop computers, tabletcomputers, servers, smart phones, etc.

Thus, the present disclosure provides an AC/DC power supply system thatincludes input transformer circuitry having a primary side and first andsecond inductively-coupled secondary sides, the primary side to receivean alternating voltage source; the first secondary side having a firstterminal and a second terminal and having a step down voltage comparedto the primary side; the second secondary side having a third terminaland a fourth terminal and having a step down voltage compared to theprimary side. The power supply system also includes first inductive cellcircuitry having a first inductive element having a first terminalcoupled to the first terminal of the first secondary side and a secondterminal coupled to a positive output terminal, and a second inductiveelement inductively coupled to the first inductive element and having athird terminal coupled to a negative output terminal and a fourthterminal coupled to fourth terminal of the second secondary side. Thepower supply system also includes second inductive cell circuitry havinga third inductive element having a fifth terminal coupled to the secondterminal of the first secondary side and a sixth terminal coupled to thepositive output terminal, and a fourth inductive element inductivelycoupled to the third inductive element and having a seventh terminalcoupled to the negative output terminal and an eighth terminal coupledto third terminal of the second secondary side. Advantageously, thepower supply system may be implemented without using output capacitorcircuitry, thus saving on cost and part count, as well as increasingoperational life of the power supply.

The terms and expressions which have been employed herein are used asterms of description and not of limitation, and there is no intention,in the use of such terms and expressions, of excluding any equivalentsof the features shown and described (or portions thereof), and it isrecognized that various modifications are possible within the scope ofthe claims. Accordingly, the claims are intended to cover all suchequivalents.

What is claimed:
 1. An AC/DC power supply system, comprising: inputtransformer circuitry having a primary side and first and secondinductively coupled secondary sides, the primary side to receive analternating voltage source; the first secondary side having a firstterminal and a second terminal and having a step down voltage comparedto the primary side; the second secondary side having a third terminaland a fourth terminal and having a step down voltage compared to theprimary side; first inductive cell circuitry having a first inductiveelement having a first terminal coupled to the first terminal of thefirst secondary side and a second terminal coupled to a positive outputterminal, and a second inductive element inductively coupled to thefirst inductive element and having a third terminal coupled to anegative output terminal and a fourth terminal coupled to fourthterminal of the second secondary side; and second inductive cellcircuitry having a third inductive element having a fifth terminalcoupled to the second terminal of the first secondary side and a sixthterminal coupled to the positive output terminal, and a fourth inductiveelement inductively coupled to the third inductive element and having aseventh terminal coupled to the negative output terminal and an eighthterminal coupled to third terminal of the second secondary side.
 2. TheAC/DC power supply system of claim 1, wherein the first and secondsecondary sides have approximately the same turns ratio with the primaryside, and the first and second secondary side are each inductivelycoupled in a same polarity to the primary side.
 3. The AC/DC powersupply system of claim 1, wherein the first inductive element and secondinductive element have approximately the same number of windings, andeach are inductively coupled in a same polarity with a positive terminalof the first inductive element being coupled to the first terminal ofthe first inductive element.
 4. The AC/DC power supply system of claim1, wherein the third inductive element and fourth inductive element haveapproximately the same number of windings, and each are inductivelycoupled in a same polarity with a positive terminal of the thirdinductive element being coupled to the fifth terminal of the thirdinductive element.
 5. The AC/DC power supply system of claim 1, whereinthe first inductive cell circuitry and the second inductive cellcircuitry have approximately the same turns ratio.
 6. The AC/DC powersupply system of claim 1, wherein the first inductive cell circuitryfurther comprising first rectifier circuitry coupled between the firstterminal of the first inductive element and the fourth terminal of thesecond inductive element.
 7. The AC/DC power supply system of claim 6,wherein the first rectifier circuitry comprises diode circuitry coupledin forward bias toward the first terminal of the first inductiveelement.
 8. The AC/DC power supply system of claim 1, wherein the secondinductive cell circuitry further comprising second rectifier circuitrycoupled between the fifth terminal of the third inductive element andthe eighth terminal of the fourth inductive element.
 9. The AC/DC powersupply system of claim 8, wherein the second rectifier circuitrycomprises diode circuitry coupled in forward bias toward the eighthterminal of the fourth inductive element.
 10. The AC/DC power supplysystem of claim 1, wherein the power supply system does not includeoutput smoothing capacitor circuitry.
 11. An AC/DC power supply system,comprising: input transformer circuitry having a primary side and firstand second inductively-coupled secondary sides, the primary side toreceive an alternating voltage source; the first secondary side having afirst terminal and a second terminal and having a step down voltagecompared to the primary side; the second secondary side having a thirdterminal and a fourth terminal and having a step down voltage comparedto the primary side; first inductive cell circuitry having a firstinductive element having a first terminal coupled to the first terminalof the first secondary side and a second terminal coupled to a positiveoutput terminal; a second inductive element inductively coupled to thefirst inductive element and having a third terminal coupled to anegative output terminal and a fourth terminal coupled to fourthterminal of the second secondary side; and first rectifier circuitrycoupled between the first terminal of the first inductive element andthe fourth terminal of the second inductive element; and secondinductive cell circuitry having a third inductive element having a fifthterminal coupled to the second terminal of the first secondary side anda sixth terminal coupled to the positive output terminal; a fourthinductive element inductively coupled to the third inductive element andhaving a seventh terminal coupled to the negative output terminal and aneighth terminal coupled to third terminal of the second secondary side;and second rectifier circuitry coupled between the fifth terminal of thethird inductive element and the eighth terminal of the fourth inductiveelement.
 12. The AC/DC power supply system of claim 11, wherein thefirst and second secondary sides have approximately the same turns ratiowith the primary side, and the first and second secondary side are eachinductively coupled in a same polarity to the primary side.
 13. TheAC/DC power supply system of claim 11, wherein the first inductiveelement and second inductive element have approximately the same numberof windings, and each are inductively coupled in a same polarity with apositive terminal of the first inductive element being coupled to thefirst terminal of the first inductive element.
 14. The AC/DC powersupply system of claim 11, wherein the third inductive element andfourth inductive element have approximately the same number of windings,and each are inductively coupled in a same polarity with a positiveterminal of the third inductive element being coupled to the fifthterminal of the third inductive element.
 15. The AC/DC power supplysystem of claim 11, wherein the first inductive cell circuitry and thesecond inductive cell circuitry have approximately the same turns ratio.16. The AC/DC power supply system of claim 11, wherein the firstrectifier circuitry comprises diode circuitry coupled in forward biastoward the first terminal of the first inductive element.
 17. The AC/DCpower supply system of claim 11, wherein the second rectifier circuitrycomprises diode circuitry coupled in forward bias toward the eighthterminal of the fourth inductive element.
 18. The AC/DC power supplysystem of claim 11, wherein the power supply system does not includeoutput smoothing capacitor circuitry.